The invention concerns steamtight forced draft gas boilers and relates especially to a new microprocessor control mode.
In steamtight forced draft gas devices one is aware that air circulation which is needed for combusion as well as simultaneously the evacuation of burnt gases is ensured by a fan since the burner and the heating body are located inside a structure protected from the local atmosphere and connected to the outside by intake and evacuation channels and that such circulation of gaseous flow can only take place naturally in conventional boilers. This fan therefore supplies an air flow, which, when the boiler is equipped with a control that includes burner flow modulation proportionate to the needs, must be dependent on the flow of gas admitted into the device or that such flow must adapt to the potential that is required and follow therefore the fluctuations in the burner gas flow. If one uses a fan at a constant rotation speed, one knows that there are bypass systems located at the level of the hood due to which part of the absorbed air is directly diverted towards the evacuation of combustible products, the amount of air admitted inside the burner thus being just enough to ensure correct combustion at the desired potential. One prefers instead of these mechanical means, to modulate the speed of the fan from a measure taken at each point of the real air flow admitted inside the burner, electronic means that ensure such a dependency. Control must therefore centralize first and foremost at each moment the exact data concerning the real air flow and the speed of the fan since one knows that there is not necessarily a precise correspondence between those two parameters, for instance in the event of clogging or obstruction of the channels.
A control system must also ensure a safety function both at the time of lighting and also during the operation phase by monitoring the temperature in various areas of the device in order to rectify the excesses or lack of temperature or to place the device at safety if need be. To that end, the control must accommodate and analyze at each moment in relation to the values of specified orders, characteristic deviation signals in relation to those values, supplied by sensors.
Those function--as well as those ensuring the control of the reverse valve for the implementation of the heating circuit or of the drawing circuit--are ensured by control systems that make use of analog circuits which transform the signals received from those various sensors into voltage or intensity variations that are compared to the specific order values inside a comparator, then amplified with an amplifier the output of which leads to the motor organ which is, for instance, the burner gas intake electromagnetic sluice gate.
Those known implementation modes, however, display some disadvantages. First of all, they use a fair amount of components and they require a special assembly. Furthermore, one knows that the specific order values are provided by the various components in use, resistances, capacities, etc.; if one wishes to alter the values, one may have to alter the components. Which means that analog control, once it is denied for a device with specific values, cannot adapt easily to other parameters without a change in the components, or, without questioning the design of the circuits. It is a serious disadvantage in the manufacturing process because often there is a need for adapting in time devices to the needs and habits of the customers while taking into account other patterned criteria, like energy savings, new safety measures, etc. Moreover, it would be difficult for this type of control to take into consideration some outer characteristics of a heating system such as the ultimate closing of all the thermostatic faucets that equip the radiators and prevent therein their discrepancies by way of the automatic introduction of time-delay on specific control cycle sequences.